1. Field of the Invention
The present invention relates generally to methods and compositions for cementing in wellbores.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in wellbores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a wellbore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hard substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the wellbore and bonds the exterior surfaces of the pipe string to the walls of the wellbore whereby the undesirable migration of fluids between zones or formations penetrated by the wellbore is prevented.
Multi-lateral wells have been developed which include vertical or deviated principal wellbores having one or more ancillary laterally extending wellbores connected thereto. Drilling and completion equipment is available which allows multiple-laterals to be drilled from a principal cased and cemented wellbore. Each of the lateral wellbores can include a liner cemented therein which is tied into the principal wellbore.
While conventional hydraulic cement compositions which are basically comprised of a hydraulic cement, e.g., Portland cement, water, and various conventional cement additives have been used successfully in primary cementing and other well cementing applications, in some well cementing applications a cement composition is required that upon setting has a higher compressive strength and lower permeability than conventional hydraulic cement compositions. Examples of well cement applications which require very high strength and very low permeability cement include, but are not limited to, cemented multi-lateral junctions, kick-off or whip-stock plugs which are placed in a wellbore to deflect the drill bit of a drill string and start directional drilling, cement plugs set on top of mechanical bridge plugs used to shut-off lower zones, plugs set in wellbores to seal the wellbores when the wells are abandoned and in remedial applications such as squeeze cementing where a cement is pressured into cracks, holes or other openings in casings or liners, cement sheaths sealing the liners in the wellbore and the like.
Thus, there are needs for improved cement compositions for use in wellbores which have very high compressive strengths and very low permeabilities.
The present invention provides improved methods and compositions for cementing in wellbores. A method of the invention for cementing in a subterranean zone penetrated by a wellbore is basically comprised of the following steps. A cement composition is provided comprised of a particulate acid degradable glass, sufficient water to form a slurry and a water soluble polyalkenoic acid. The cement composition is placed in the subterranean zone by way of the wellbore after which the cement composition is allowed to set into a strong impermeable solid cement mass in the subterranean zone.
Another method of the invention is basically comprised of the following steps. A cement composition is provided comprised of particulate acid degradable glass, sufficient water to form a slurry, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical initiator. The cement composition is placed in the subterranean zone by way of the wellbore after which the cement composition is allowed to set into a strong impermeable solid cement mass in the subterranean zone. The cement composition sets as a result of the free-radical polymerization initiator causing the alkenoic acid monomer to polymerize and react with the acid degradable glass.
A well cement composition of this invention is basically comprised of particulate acid degradable glass, sufficient water to form a slurry, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical initiator.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
The present invention provides improved methods and compositions for cementing in subterranean zones penetrated by wellbores. The cement compositions can be elastic or they can have very high compressive strength and very low permeability. The methods and cement compositions of this invention are useful in a variety of well cementing applications such as cementing multi-lateral junctions, forming kick-off or whip-stock plugs in wellbores to deflect drill bits and start directional drilling, cementing bridge plugs in wellbores to shut off lower zones, cementing wellbores to form plugs therein when the wellbores are abandoned and remedial applications in wellbores whereby holes, cracks and the like in casing and cement are repaired by squeeze cementing techniques. A quick setting cement composition which can be utilized in accordance with the methods of this invention is basically comprised of particulate acid degradable glass, sufficient water to form a slurry and a water soluble polyalkenoic acid. The polyalkenoic acid reacts with the particulate acid degradable glass and relatively quickly sets and forms a strong impermeable solid cement.
An improved cement composition of this invention which can be utilized in applications in which the set of the cement composition must be delayed to allow its placement in a subterranean zone is basically comprised of a particulate acid degradable glass, sufficient water to form a slurry, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical polymerization initiator.
The particulate acid degradable glass is different from well-known soda-lime glass. Acid degradable glass is a calcium alumino silicate material which is a commercially available glass that is mixed with fluoride and utilized in dental applications. The fluoride in the acid degradable glass used by dentists is for preventing tooth decay and is not necessary in well applications. Calcium alumino silicate glass is also available as a slag by-product from coal gasification processes. As the name implies, acid degradable glass is degraded by and reacts with certain acids when in contact therewith. The acid degradable glass is present in the cement compositions described above in an amount in the range of from about 2.5% to about 85% by weight of the composition.
The water in the cement compositions of this invention can be fresh water or saltwater. The term xe2x80x9csaltwaterxe2x80x9d is used herein to mean unsaturated salt solutions and saturated salt solutions including brines and seawater. The water is present in the cement compositions in an amount in the range of from about 10% to about 40% by weight of the compositions.
The water soluble polyalkenoic acids which can be utilized in the quick setting cement compositions described above include, but are not limited to, homopolymers or copolymers of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and butene-1,2,3-tricarboxylic acid. Of these, polyacrylic acid or polymethacrylic acid is preferred. The polyalkenoic acid is present in the cement compositions in an amount in the range of from about 5% to about 15% by weight of the compositions.
The water soluble polymerizable alkenoic acid monomer or monomers in the delayed set compositions of this invention can be alkenoic acid monomers selected from the group consisting of acrylic acid, itaconic acid, maleic acid, methacrylic acid, 3-butene-1,2,3-tricarboxylic acid and mixtures thereof. Of these, acrylic acid or methacrylic acid is preferred. The one or more water soluble ailcenoic acid monomers can be alkenoic acid esters which are delayed by requiring hydrolysis before polymerizing and reacting with the acid degradable glass. Examples of the alkenoic acid esters which can be utilized include, but are not limited to, hydroxyethyl acrylate ester, hydroxyethyl methacrylate ester, hydroxypropyl acrylate ester, hydroxypropyl methacrylate ester and mixtures thereof. Of these, hydroxyethyl acrylate ester is preferred. The one or more water soluble polymerizable alkenoic acid monomers or esters utilized are included in the cement compositions of this invention in an amount in the range of from about 5% to about 15% by weight of the compositions.
A variety of water-soluble free-radical polymerization initiators can be utilized in the delayed set compositions. A particularly suitable type of free-radical initiator is an azo polymerization initiator. Azo polymerization initiators are defined by the formulas set forth in detail in U.S. Pat. No. 5,335,726 issued to Rodrigues on Aug. 9, 1994 which is incorporated herein by reference thereto. The azo polymerization initiators are commercially available from Wako Pure Chemical Industries, Ltd. of Osaka, Japan and Wako Chemicals USA, Inc. of Richmond, Va. The azo initiators have 10 hour half-lives at temperatures ranging from about 110xc2x0 F. to about 220xc2x0 F. Accordingly, by determining the temperature of the formation into which the cement composition of this invention is to be placed and the required pumping time, an azo initiator type and concentration can be selected for polymerization initiation which provides an induction period sufficient to allow the cement to be placed.
Particularly suitable azo free radical initiators include, but are not limited to, 1-[(1-cyano-1-methylethyl)azo]formamide (10 hour half life temperature 219xc2x0 F.), 2,2xe2x80x2-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride (10 hour half life temperature 106xc2x0 F.), 2,2xe2x80x2-azobis(2-methylpropionamidine) dihydrochloride (10 hour half life temperature 133xc2x0 F.), 2,2xe2x80x2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (10 hour half life temperature 111xc2x0 F.), 2,2xe2x80x2-azobis[2-methyl-N-(2-hydroxy-ethyl)propionamide] (10 hour half life temperature 187xc2x0 F.) and 4,4xe2x80x2-azobis(4-cyanovaleric acid) (10 hour half life temperature 156xc2x0 F.).
When an alkenoic acid or a delayed alkenoic acid ester is utilized in the cement compositions, the water-soluble free-radical initiator can be an oxidizing compound. Examples of such oxidizing free-radical initiators include, but are not limited to, sodium persulfate, ammonium persulfate, t-butylhydroperoxide and hydrogen peroxide with or without a reducing agent selected from the group consisting of sodium thiosulfate, sodium bisulfite and triethanolamine.
Generally, the water soluble free-radical initiator utilized is present in the cement compositions in an amount in the range of from about 0.001% to about 0.25% by weight of the compositions.
The quick set and delayed set cement compositions can also include a filler comprised of silica flour or powdered iron oxide. When used, the filler is present in the cement compositions in an amount in the range of from about 10% to about 1900% by weight of the acid degradable glass therein. The presence of relatively large amounts of filler in the cement compositions makes the cement compositions elastic. For example, when a cement composition of this invention includes a ratio of iron oxide filler to acid degradable glass in the range of from about 3:1 to about 19:1, the resulting set cement composition has elastic properties.
The methods of this invention for cementing in a subterranean zone penetrated by a wellbore are basically comprised of the following steps. A cement composition is provided comprised of particulate acid degradable glass, sufficient water to form a slurry, and a polyalkenoic acid, or alternatively when it is necessary to delay the set of the cement composition, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical initiator. The cement composition is placed in a subterranean zone to be cemented and then allowed to set into a strong impermeable solid cement mass in the subterranean zone.
The mechanism by which the delayed set cement compositions of this invention set is as follows. The free-radical polymerization initiator causes the one or more alkenoic acid monomers to polymerize. The resulting alkenoic acid polymer then reacts with the acid degradable glass to form a strong impermeable solid cement mass. While the alkenoic acid monomer or monomers may react with the acid degradable glass prior to the polymerization, that reaction does not cause a set.
A preferred method of this invention for cementing in a subterranean zone penetrated by a wellbore where a quick set is required comprises the steps of: (a) providing a cement composition comprised of particulate acid degradable glass, sufficient water to form a slurry and a water soluble polyalkenoic acid; (b) placing the cement composition in the subterranean zone; and (c) allowing the polyalkenoic acid to react with the acid degradable glass and set into a strong impermeable solid cement mass in the zone.
Another preferred method of the present invention for cementing in a subterranean zone penetrated by a wellbore where a delayed set is required comprises the steps of: (a) providing a cement composition comprised of particulate acid degradable glass, sufficient water to form a slurry, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical initiator; (b) placing the cement composition in the subterranean zone; and (c) allowing the free-radical initiator to cause the alkenoic acid monomer to polymerize and react with the acid degradable glass and set into a strong impermeable solid cement mass in the zone.
A preferred well cement composition of this invention is comprised of particulate acid degradable glass, sufficient water to form a slurry, at least one water soluble polymerizable alkenoic acid monomer and a water soluble free-radical initiator.
In order to further illustrate the methods and compositions of this invention the following example is given.